Revisiting Singles vs. Doubles- This time with Mice

Back in the day, the importance of a distance run was thought to be that of putting constant pressure on the heart so that it will adapt. In other words the theory went that you wanted to keep your heart rate up for a prolonged period. So the logic went, the further we can go the better.

What we now know is that adapting to training is a super complicated process that involves numerous different adaptations on multiple different systems. So is it as easy as more is always better? I’ve delved into this question many times in regards to doubles versus singles. By the old school logic, singles should always be better. It makes logical sense that 10 miles once is better than 5 miles twice. But as I pointed out before, that logic isn’t always sound. It’s one of my favorite topics to delve into (more here) and it’s always worth looking into.

An interesting new study came out where they took a look at the effect of one 30min run versus 3x10min runs throughout the day in mice. It’s not quite your doubles versus singles argument, but it’s an interesting concept.

What makes the research a bit more fascinating (and also harder to translate to real world application) is that it was on mice, which means they could dissect and analyze all sorts of things that we normally can’t see. We get to see what is going on at the cellular level instead of relying on crappy surrogate markers like VO2max.

What they did was take mice and stick them on an 8 week treadmill training regime. Half the group they had do 30min a day all at once 5x a week, while the others did 3x10min split with 2 hours rest in between. Then they measured all sorts of lovely signaling pathways activation to see what was going on.

What did they find?

Performance- Pre and post training Each group improved their distance covered from 224 to 464 (30min) and 217 to 471 (3x10min), speed, and work to similar levels.

Capillary- Both groups had similar increases in capillarization. No significant differences between the two groups.

Pathways- Citrate Synthase activity increased in both groups to similar levels and VEGFR2 increased similarly in both groups. Slow Twitch fiber % increased in both. TSP-1 decreased by 50% in the 30min group and 68% in the 3x10min group. P38 MAPK increased similarly in both.

What do these random letter combination things mean?

VEGFR2 refers to one of the receptor for vascular endothelial growth factor (VEGF-A) which is basically one of the regulators for capillarization. TSP-1 is the protein that essentially works in contrast to VEGF-A. So if you get a decrease in TSP-1, you generally get an increase in capillarization. So taken together, increase in VEGF and decrease in TSP-1 in this study meant increase in capillaries. P38 MAPK is involved in the PGC-1 pathway which regulates mitochondria proliferation among other endurance related changes.

So what?

Yes, it’s only mice. But what is interesting about this study is that you saw similar increases in performance, capilarization, and mitochondrial biogenesis. This would run in the face of the old school running/training thought process. It doesn’t mean everyone should get out and start training three times a day and never run far. What I think it does do is give just a little more evidence for why doubling (or maybe tripling?) may work. And before I get crucified by the old school singles are king people. All I’m saying is that maybe each has their place and this study simply adds intrigue to the idea.

In my own coaching, I’m a big fan of the occasional even split short double for recoveries sake and if studies like these are to believed you’re not really missing out on the stimulus for adaptation. Just judging by past experience that was always my feeling with the high school kids I used to coach ( Running Times article here) We’d do singles for the most part in the summer and then doubles during the school year because there were only so many times you could run around the boring loop at school without wanting to kill yourself. What I found was that endurance was maintained as long as they had a single long run on the weekend.

So what’s that mean? I have no idea. But maybe to build endurance we go with singles and shift to more doubles which are easier on the body for maintenance. Then the question gets asked about other forms of exercise or what is the effect of doing cross training as a shakeout or a shakeout after a workout, or on and on. So many questions, so much to figure out.

Periodize your easy runs? Maybe. Most of the time we just ignore easy/distance runs and don’t put much thought into them. Maybe it’s time to.

11 thoughts on “Revisiting Singles vs. Doubles- This time with Mice”

From reading an interview with Mike Morton after Badwater he talks about the doubles being a big bulk of his training. He mentions doing 12 miles at lunch followed by anotehr 13-15 at night to help the adapation. Of course that is an extreme and Morton is a freak, but he's done pretty good wtih it.

Am I missing something when they say distance covered improved by similar levels? The 3x10min group had a 117.05% improvement while the 1x30min group was 107.14%. Possible conclusions I came up with are a gap of 10% either wasn't large enough to affect the statistical significance "p" or they could chalk up the marginally longer distance by the 3x10min group to having rest periods and being able to run at a higher average speed.

Rest, specifically being a high or low responder to a given amount of recovery time, seems like an important factor to weigh when debating singles vs. doubles in our own training/coaching.

Galloway and others advocate walking every mile or so to break up long runs which supposedly decreases recovery time with little to no loss of fitness adaptation. This doubles research seems to add credence to the benefits of these walking breaks.

The cross country team I help coach, started this year running doubles to get more miles for the same reasons as you outlined in the RunningTimes article. We saw great gains at the end of the year in all of our athletes. Now these gains could have been from other workouts or a combination of many variables. However, the kids saw and believed that everything helped them get faster. The attendance at the early runs increased because the others did not want to get left behind. The athletes seemed to run faster too when the distances were split verses if the miles were done all at once.

Wouldn't running singles vs. doubles effect which energy system one was using? For example, running a single 1:30 run without taking carbohydrate during the run would adapt the body to fat metabolism better than doing two :45 minute runs. This could be more advantageous for someone looking to run a marathon for instance. Or do I have that wrong?

Would doing doubles be beneficial when returning from injury and transitioning to longer Miles/Kms again. I have found doing 2 x 5 mile runs or a 6 and a 4 mile run a lot easier on my body than doing an 10 mile run (for achilles problems anyway)

It's good to read that doubles showed those results, because I find it easier and more enjoyable to run splits or doubles vs a long single run. Makes me feel better about things. Thanks for the very interesting article.

Sorry for this being completely unrelated- I am a high schooler running 45-60 miles per week. During my long run, 10-13 miles, I like to stop at the YMCA with 3 miles left in my run and strength train for 15-25 minutes just to break up the monotony. My long run/strength looks something like this- 8 miles, 3×5 Squat, 10 Pull ups, 10 Dips, 30 Push ups, 3×5 Clean, 10 Pull ups, 10 Dips, 30 Push ups, 3 miles. Is adding strength in my long run more beneficial or detrimental?

I'm really interested in the singles vs doubles arguments. I'm a fairly new (just over 3 years of running) marathon runner, peaking at 85MPW. I follow Daniels, and he suggests doing doubles as soon as 50MPW.

I think your table is a bit off with regards to your comment of "it's pointless to put on the shoes for 25 minutes"? The 75MPW column has singles of 9/13/9/13/9 during the week, after a 15 long run. I do a lot of double 6's, which at my paces are around 45-50 minutes, not 25 minutes. My point is it's possible to double at less than 80 MPW without reducing every run to 25 minutes.

The other factor with doubles is that for people with work and family commitments, 2 runs of 45 to 60 minutes are generally a lot more practical than a single run of 90 to 120 minutes. Personally, I could not find time for 80MPW in singles, so for me, doubles are a necessity. What I mean is that sometimes the argument is not "12 vs 2×6", but "9 vs 2×6", in which case for me doubles win out.